The fact has been known that temperatures of batteries during their operations may affect their lifetime and charge-discharge efficiencies. More specifically, elevated temperatures accelerate breakdown of electrolytes in a battery and may shorten the lifetime of the battery due to deterioration, whereas lowered temperatures depress reactivity of the electrodes and may worsen the charge-discharge efficiency. For preventing any reduction in the lifetime or degradation of the charge-discharge efficiency, it is of an importance to keep the temperature of a battery within its optimal temperature range.
In an electric vehicle, the temperature of a battery may be elevated due to heat generation during repeated charge-discharge cycles in the battery, and one known strategy for controlling the battery temperature is to provide an evaporator within a casing receiving the battery, such that the evaporator cools the air inside the casing. The air cooled by the evaporator is circulated through the casing and removes heat from the battery, thereby cooling the battery to its optimal temperature.
In contrast, in electric vehicles tailored to cold climate areas (hereinafter, such vehicles may also be referred to as “cold-climate vehicles”), for example, a battery may be cooled below its optimal temperature range when the vehicle is powered off. Hence, in some electric vehicle tailored to cold climate areas, the battery shall be heated up to its optimal temperature when the temperature of the battery is low.
As an example, Patent Literature 1 (Japanese Laid-Open Patent Application No. 2010-285110) discloses a technique for increasing a temperature of a battery by repeating alternative discharge and charge of the battery, when the battery temperature is lower than a predetermined value. As another example, Patent Literature 2 (Japanese Laid-Open Patent Application No. 2013-171663) discloses a technique for heating a battery with a heater provided within a casing receiving the battery by heating the air inside the casing using that heater. Such a heater may be employed to increase the battery temperature in a short time.
Unfortunately, as discussed in Patent Literature 2, for example, provision of a heater requires extra parts used for attaching the heater to the casing and extra space used for receiving the heater inside the casing. Hence, providing a heater to a cold-climate vehicle requires redesign of the casing and additional parts for attaching the heater, which increases the manufacturing cost. Furthermore, battery heaters are not parts for standard vehicles which are not tailored to cold climate areas (hereinafter, such vehicles may also be referred to as “standard vehicles”), but are parts optional to cold-climate vehicles. It is therefore difficult to use common parts in both vehicles with and without in-casing heaters, and to improve the efficiency of the assembly.